std::bind
参考资料
• cplusplus.com:http://www.cplusplus.com/reference/functional/bind/
• cppreference.com:http://en.cppreference.com/w/cpp/utility/functional/bind
std::bind简介
• 函数模板声明
// cplusplus.com // simple(1) template <class Fn, class... Args>
/* unspecified */ bind (Fn&& fn, Args&&... args);
// with return type (2)
template <class Ret, class Fn, class... Args>
/* unspecified */ bind (Fn&& fn, Args&&... args);
// GCC 4.8.2 - /usr/include/c++/4.8.2/tr1
template <typename _Functor, typename... _ArgTypes>
inline _Bind<typename _Maybe_wrap_member_pointer<_Functor>::type(_ArgTypes...)>
bind(_Functor __f, _ArgTypes... __args)
{
...
}
template <typename _Result, typename _Functor, typename... _ArgTypes>
inline _Bind_result<_Result, typename _Maybe_wrap_member_pointer<_Functor>::type (_ArgTypes...)>
bind(_Functor __f, _ArgTypes... __args)
{
...
}
// MS C++ 2013 \Microsoft Visual Studio 12.0\VC\include\functional
template <class _Fun, class... _Types>
inline _Bind<false, void, _Fun, _Types...>
bind(_Fun && _Fx, _Types &&... _Args)
{ // bind a function object
...
}
template <class _Rx, class... _Ftypes, class... _Types>
inline _Bind<true, _Rx, _Rx (* const)(_Ftypes...), _Types...>
bind(_Rx (*_Pfx)(_Ftypes...), _Types&&... _Args)
{ // bind a function pointer
...
}
template <class _Rx, class _Farg0, class... _Types>
inline _Bind<false, void, _Pmd_wrap<_Rx _Farg0::*, _Rx, _Farg0>, _Types...>
bind(_Rx _Farg0::* const _Pmd, _Types&&... _Args)
{ // bind a wrapped member object pointer
...
}
#define _IMPLICIT_PMF_WRAP(CALL_OPT, X1, CV_OPT) \
template <class _Rx, class _Farg0, class... _Ftypes, class... _Types> \
inline _Bind<true, _Rx, _Pmf_wrap<_Rx(CALL_OPT _Farg0::*)(_Ftypes...) CV_OPT, _Rx, _Farg0, _Ftypes...>, _Types...> \
bind(_Rx(CALL_OPT _Farg0::* const _Pmf)(_Ftypes...) CV_OPT, _Types&&... _Args) \
{ /* bind a wrapped CV_OPT member function pointer */ \
...
}
_MEMBER_CALL_CV(_IMPLICIT_PMF_WRAP, )
...
• 函数模板说明
以cplusplus.com中描述的原型说明:
基于Fn参数返回一个函数对象,并且以Args参数绑定为函数对象的参数。每个参数要么绑定一个参数值,要么绑定为一个std::placeholders。如果参数绑定成一个值,那么返回的函数对象将总使用绑定的参数值做为调用参数,即调用传入参数将不起作用;如果参数绑定为std::placeholders,那么返回的函数对象在被调用时需要传入实时参数,参数填充的位置即由placeholder指定的序号。
bind函数返回的函数对象类型和Fn一致,除非用户在Ret参数中指定了返回类型。需要注意的是,Ret参数只是一个模板参数,它并不能由传入该函数的参数进行隐式推导。
• 模板参数说明
以cplusplus.com中描述的原型说明:
Fn : 函数对象、普通函数指针或类成员函数指针。
Args : 用于绑定的参数列表。其中每个参数要么是参数值要么是一个placeholder
std::bind详解
• 绑定普通函数
#include <iostream> #include <functional> using namespace std; int g_Minus(int i, int j) { return i - j; } int main() { function<int(int, int)> f1 = bind(g_Minus, 1, 2); function<int()> f2 = bind(g_Minus, 1, 2); // 绑定参数返回的函数对象实际等同这种形式 function<int(int, int)> f3 = bind(g_Minus, placeholders::_1, placeholders::_2); function<int(int)> f4 = bind(g_Minus, 1, placeholders::_1); // 绑定第一个参数 function<int(int)> f5 = bind(g_Minus, placeholders::_1, 1); // 绑定第二个参数 cout << f1(3, 2) << endl; // -1,实际传入参数将不起作用 cout << f2() << endl; // -1 cout << f3(3, 2) << endl; // 1 cout << f4(3) << endl; // -2 cout << f5(3) << endl; // 2
return 1; }
• 绑定模板函数
#include <iostream> #include <functional> using namespace std; template <class T> T g_Minus(T i, T j) { return i - j; } int main() { function<int(int, int)> f1 = bind(g_Minus<int>, 1, 2); function<int()> f2 = bind(g_Minus<int>, 1, 2); // 绑定参数返回的函数对象实际等同这种形式 function<int(int, int)> f3 = bind(g_Minus<int>, placeholders::_1, placeholders::_2); function<int(int)> f4 = bind(g_Minus<int>, 1, placeholders::_1); // 绑定第一个参数 function<int(int)> f5 = bind(g_Minus<int>, placeholders::_1, 1); // 绑定第二个参数 cout << f1(3, 2) << endl; // -1,实际传入参数将不起作用 cout << f2() << endl; // -1 cout << f3(3, 2) << endl; // 1 cout << f4(3) << endl; // -2 cout << f5(3) << endl; // 2 return 1; }
• 绑定lambda表达式
#include <iostream> #include <functional> using namespace std; int main() { function<int(int, int)> f = bind([](int i, int j){ return i - j; }, placeholders::_1, placeholders::_2); cout << f(2, 3) << endl; // -1 return 1; }
• 绑定函数对象
#include <iostream> #include <functional> using namespace std; struct Minus { int operator() (int i, int j) { return i - j; } }; int main() { function<int(int, int)> f = bind(Minus(), placeholders::_1, placeholders::_2); cout << f(2, 3) << endl; // -1 return 1; }
• 绑定类静态成员函数
#include <iostream> #include <functional> using namespace std; class Math { public: static int Minus(int i, int j) { return i - j; } }; int main() { function<int(int, int)> f = bind(&Math::Minus, placeholders::_1, placeholders::_2); cout << f(2, 3) << endl; // -1 return 1; }
• 绑定类对象成员函数
#include <iostream> #include <functional> using namespace std; class Math { public: int Minus(int i, int j) { return i - j; } }; int main() { Math m; function<int(int, int)> f = bind(&Math::Minus, &m, placeholders::_1, placeholders::_2); cout << f(2, 3) << endl; // -1 return 1; }
• 返回值的类型转换
#include <iostream> #include <functional> using namespace std; class Math { public: int Minus(int i, int j) { return i - j; } }; struct Result { int m_Result; Result() : m_Result(0) {} Result(int result) : m_Result(result) {} }; int main() { Math m; auto f = bind<Result>(&Math::Minus, &m, placeholders::_1, placeholders::_2); Result r = f(2, 3); cout << r.m_Result << endl; // -1 return 1; }